Positively chargeable toner

Abstract

A positively chargeable toner includes toner particles. Each of the toner particles includes a composite core and a shell layer covering a surface of the composite core. Each of the composite cores is a composite of a toner core containing a binder resin and a colorant layer disposed over a surface of the toner core. The colorant layers contain carbon black. The colorant layers have a thickness of at least 200 nm and no greater than 500 nm. The shell layers include a repeating unit having a non-ring-opened oxazoline group. An amount of the non-ring-opened oxazoline group contained in 1 g of the positively chargeable toner as measured by gas chromatography-mass spectrometry is at least 500 μmol and no greater than 1,000 μmol.

What is claimed is: 
     
       1. A positively chargeable toner comprising toner particles, wherein
 each of the toner particles includes a composite core and a shell layer covering a surface of the composite core, 
 each of the composite cores is a composite of a toner core containing a binder resin and a colorant layer disposed over a surface of the toner core, 
 the colorant layers contain carbon black, 
 the colorant layers have a thickness of at least 200 nm and no greater than 500 nm, 
 the shell layers include a repeating unit having a non-ring-opened oxazoline group, and 
 an amount of the non-ring-opened oxazoline group contained in 1 g of the positively chargeable toner as measured by gas chromatography-mass spectrometry is at least 500 μmol and no greater than 1,000 μmol. 
 
     
     
       2. The positively chargeable toner according to  claim 1 , wherein
 the repeating unit having a non-ring-opened oxazoline group is a repeating unit represented by formula (1-1) shown below, 
 
       
         
           
           
               
               
           
         
         where in formula (1-1), R 1  represents a hydrogen atom or an alkyl group optionally substituted with a phenyl group. 
       
     
     
       3. The positively chargeable toner according to  claim 1 , wherein
 the carbon black contained in the colorant layers is an acidic carbon black. 
 
     
     
       4. The positively chargeable toner according to  claim 3 , wherein
 the acidic carbon black has a pH of at least 2.5 and no greater than 5.0. 
 
     
     
       5. The positively chargeable toner according to  claim 1 , wherein
 the binder resin includes a polyester resin, and 
 the polyester resin has an acid value of at least 5 mgKOH/g. 
 
     
     
       6. The positively chargeable toner according to  claim 1 , wherein
 the colorant layers have a thickness of at least 350 nm and no greater than 500 nm, 
 the carbon black contained in the colorant layers is an acidic carbon black having a pH of at least 3.0 and no greater than 4.0, and 
 the amount of the non-ring-opened oxazoline group is at least 700 μmol and no greater than 1,000 μmol.